Answer to Question #283898 in Mechanics | Relativity for straus

Question

A 3500-kg car hits an 80-kg pedestrian who is standing in the middle of the road. Before the collision, the car was travelling at 30 km/h and the pedestrian was stationary. After the collision, the car was traveling at 28.5 km/h. At what speed will the pedestrian be flung down the road (in km/h)

Answer 1

mass of Car $(M_c)=3500kg$

Mass of pedestrian$(M_p)=80kg$

Initial velocity before collision

$$V_c=30km/hr=\frac{30\times1000}{3600}m/sec=\frac{150}{18}m/sec\\v_p=0km/hr$$

After collision

$$V'_c=28.5km/hr=\frac{28.5\times1000}{3600}m/sec=\frac{1425}{180}m/sec$$

Momentum conservation

Momentum Before collision= momentum after collision

$M_cV_c+M_pV_p=M_cV'_c+M_pV'_p$

Put value

$$3500\times\frac{150}{18}+80\times0=3500\times\frac{1425}{180}+80\times V'_p$$

$29166.66=27708.33+80V'_p$

$1458.33=80V'_p\\V'_p=28.2291m/sec$